Methods for using sulfidized red mud

ABSTRACT

Toxic substances such as heavy metals are extracted from a medium using a sorbent composition. The sorbent composition is derived by sulfidation of red mud, which contains hydrated ferric oxides derived from the Bayer processing of bauxite ores. Exemplary sulfidizing compounds are H 2 S, Na 2 S, K 2 S, (NH 4 ) 2 S, and CaS x . The sulfur content typically is from about 0.2 to about 10% above the residual sulfur in the red mud. Sulfidized red mud is an improved sorbent compared to red mud for most of the heavy metals tested (Hg, Cr, Pb, Cu, Zn, Cd, Se, Th, and U). Unlike red mud, sulfidized red mud does not leach naturally contained metals. Sulfidized red mud also prevents leaching of metals when mixed with red mud. Mixtures of sulfidized red mud and red mud are more effective for sorbing other ions, such as As, Co, Mn, and Sr, than sulfidized red mud alone.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No.12/781,965, filed May 18, 2010, which is a division of U.S. applicationSer. No. 12/537,907, filed Aug. 7, 2009, now U.S. Pat. No. 7,807,058,which is a division of U.S. application Ser. No. 11/277,282, filed Mar.23, 2006, now U.S. Pat. No. 7,763,566, the disclosures of which arehereby incorporated by reference. The disclosure of U.S. applicationSer. No. 12/796,066, filed Jun. 8, 2010, and being acontinuation-in-part of application Ser. No. 11/277,282, filed Mar. 23,2006, now U.S. Pat. No. 7,763,566, is also incorporated hereinto byreference.

FIELD OF THE INVENTION

The present invention is generally directed to sorbents and methods foruse of said sorbents in the treatment of fluids such as waste streams toremove undesired contaminants contained therein and particularly for thefacile extraction of heavy metals inter alia from liquid and gaseousstreams, as well as removal of the sorbed heavy metals by solids/fluidseparation means.

DESCRIPTION OF RELATED ART

Heavy metal contaminated flue gases and liquids from various sources(ground, stream, runoff, mines, petroleum, industrial waste, sanitarywaste) are among the most dangerous and difficult environmental problemsfacing the world today. An especially serious problem is posed by toxicmetals in such streams. Among these metals are mercury, chromium,cobalt, nickel, copper; zinc, silver, gold, cadmium, lead, selenium, andtransuranic elements.

Mercury contamination of the environment is the subject of increasingattention because it eventually accumulates at very high levels in thebodies of large predatory fish such as tuna, swordfish, and sharks. Amajor concern is the atmospheric release of mercury from coal firedpower plants, currently estimated at 46 tons per year in the UnitedStates. The Environmental Protection Agency (EPA) has identified womenof childbearing age as especially threatened because of possibleneurological damage to unborn children. It has been estimated that 8% ofwomen in this category have a methyl mercury blood level above 5.8 ppb.

On Dec. 14, 2000, the EPA issued a determination that their agency mustpropose new regulations under the Clean Air Act to control mercuryemissions from coal and oil fined power plants by Dec. 15, 2003. Oneproposal was to reduce mercury emissions from power plants by 90% by2007. According to an article in Forbes (Apr. 14, 2003, page 104) suchregulation “could cost the power industry at least 8.8 billion dollarsper year.” Other, more recent proposals such as the Clear Skies Act callfor a 70% reduction in mercury emissions over 15 years.

At present, a major control technology for mercury is the use ofactivated carbon treatment of flue gases from power plants. Activatedcarbon currently sells for about 45 cents per pound ($900 per ton) butthe disposal or possible regeneration of mercury-sorbed activated carbonpresent unresolved problems at this time.

Red mud is an undesirable by-product and major pollutant from the BayerProcess. Bayer caustic leaching of bauxite is the principal process forproduction of alumina. This process relies on the solubility ofaluminous minerals in hot (e.g., 125-250° C.) sodium hydroxide solutionand the insolubility of most of the remaining minerals (iron, titaniumcompounds and silica), which are either insoluble or react andre-precipitate. The insoluble, iron rich residue byproduct is known as“red mud.” Red mud can contain from about 17.4 to 37.5% iron (Fe)(Bauxite Residue Fractionation with Magnetic Separators, D. WilliamTedder, chapter 33, Bauxite symposium, 1984, AIME 1984). Red mud is acomplex mixture of finely divided hydrated iron oxides with a widevariety of lesser minerals (Al, Na, Ti, Si, Ca, Mg) and traces of over ascore of other elements (Cr, Ni, Zn, Pb, As, etc). These hydrous ironoxides have extraordinary sorptive and complexing properties.

Red mud is a very hydrophilic, high pH slime which is extremelydifficult to dewater by filtration or sedimentation means. Thiscomplicates and limits its utility as a sorbent in aqueous systems.

Red mud has been proposed as a sorbent for heavy metals, cyanides,phosphates, and the like (David McConchie, Virotec website:virotec.com/global.htm). However, the sorptive and release properties ofred mud are not always complementary. Depending on the source of aparticular red mud, it can also leach out significant amounts of toxicpollutants such as radioactive thorium, uranium, chromium, barium,arsenic, copper, zinc, cobalt and selenium, as well as lead, cadmium,beryllium, and fluorides.

The potential problems involved with use of red mud to control pollutionare highlighted in an e-newsletter article entitled “The Great Red MudExperiment that Went Radioactive”—Gerard Ryle, May 7, 2002(smh.com.au/articles/2002/05/06/1019441476548.html). This experimentconducted by the Western Australian Agricultural Department involvedplacing 20 tonnes of Alcoa red mud per hectare on farmland in order tostop unwanted phosphorous from entering waterways. An unintended resultof this application was that runoff waters showed excessive quantitiesof copper, lead, mercury, arsenic, and selenium. Emaciated cattlegrazing on such land exhibited high chromium, cadmium, and fluoridelevels. Each hectare contained up to 30 kilograms of radioactivethorium. The disastrous red mud application test was abruptly terminatedafter five years.

It is therefore evident that extreme caution must be exercised inselecting and testing red mud before attempting to use it to sorb toxiccompounds.

Furthermore, the capacity of red mud to capture and hold toxicsubstances such as mercury and related metals is not adequate toeliminate traces of these metals in leachate. The possibility alsoexists that sorption of one toxic pollutant may release otherpollutants. As a result, use of red mud as a sorbent to achieve drinkingwater standards can be problematic.

Prior attempts to produce useful materials from red mud are exemplifiedby Yu et al in U.S. Pat. No. 4,560,465. In this patent, Yu et aldisclose the presulfiding of red mud using hydrogen and H₂S inter aliaat temperatures ranging from about 200° F. to 3000° F. and pressuresranging from 50 to 3500 psig, these conditions being sufficiently severeto convert substantially all of the iron, namely, both Fe₂O₃ and the Fe,Al, Ca oxide hydrates, to pyrrhotite, Fe_(1-x)S, and particularly Fe₇S₈.The pyrrhotitic material thus formed is dehydrated and is less reactiveas a sorbent than is red mud per se. The pyrrhotitic materials of Yu etal are used as a catalytic agent for cracking hydrocarbons, thesematerials apparently providing a more efficient hydrogen distributionfor the catalyst of Yu et al as noted in column 4, lines 36-40 of theaforesaid patent. The red mud products treated according to the teachingof Yu et al are ineffective for use as sorbents.

Sulfidized red mud prepared according to the invention, that is, underrelatively mild conditions compared to the severe temperatures andpressures of Yu et al as well as without the use of hydrogen, is anamorphous material useful as a sorbent which typically does not containpyrrhotites as does the catalyst of Yu et al which is not useful as asorbent.

There remains a need for improved sorbents for extracting toxiccompounds such as mercury and other heavy metals from waste streams andthe like and for extracting undesirable contaminants from other fluids.

SUMMARY OF THE INVENTION

The present invention, according to one aspect, is directed to a sorbentcomprising the reaction product of a sulfidizing compound and red mud.Red mud contains hydrated ferric oxides derived from Bayer processing ofbauxitic ores. The sorbent is particularly useful for sorbing toxicsubstances from a medium, such as heavy metals present in a liquid orgaseous stream. Exemplary sulfidizing compounds include H₂S, Na₂S, K₂S,(NH₄)₂S, and CaS_(x). The sulfur content of the reaction producttypically is from about 0.2 to about 10% above the residual sulfur inthe red mud.

According to one aspect of the invention, potable water (e.g., meetingdrinking water standards) is prepared by treating contaminated waterwith a sulfidized red mud sorbent.

According to another aspect of the invention, heavy metals, whether inelemental or ionic form, such as mercury are sorbed from flue gases ofcoal- or oil-fired power plants by treating the flue gases with asulfidized red mud sorbent. Other applications include but are notlimited to treatment of waste effluents from municipal waste combustors,hazardous waste combustors, hospital waste combustors, cement kilns, andindustrial boilers inter alia.

According to another aspect of the invention, heavy metals are sorbedfrom mine drainage waters by treating the mine drainage waters with asulfidized red mud sorbent.

According to yet another aspect of the invention, heavy metals aresorbed from a hydrocarbon stream, such as a petroleum stream, bytreating the stream with a sulfidized red mud sorbent.

The sorbent of the present invention is more effective for sorbingvarious contaminants, such as mercury, which are less effectively sorbedby red mud. Conversely, red mud is effective for sorbing othercontaminants, such as arsenic, which are not effectively sorbed by thesulfidized red mud sorbent. Thus, some treatments can benefit by usingboth red mud and sulfidized red mud, either in the same sorbentcomposition or in separate treatment stages. Such sorbent combinationspotentially can allow for the extraction of a wider range ofcontaminants.

Sulfidized red mud as disclosed herein is an effective sorbent forremoving a wide variety of noxious materials from fluids ranging fromcontaminated water to flue gases and further permits more facilerecycling of caustic liquors in aluminum production by sulfidizing redmud resulting from such processes.

DETAILED DESCRIPTION OF THE INVENTION

The present invention has applicability in removing contaminants from awide variety of mediums, non-limiting examples of which include fluegases and liquids from various sources such as groundwater, waterstreams, sanitary waste waters, runoff, mines, petroleum streams, andindustrial waste streams. Of particular interest is sorbing heavymetals, such as mercury (Hg), chromium (Cr), lead (Pb), copper (Cu),zinc (Zn), silver (Ag), gold (Au), cadmium (Cd), selenium (Se), thorium(Th), and uranium (U), from such mediums. The metal(s) may be present asions, as free elements, or in compounds with other elements.

The sorbents of the present invention can be used for the preparation ofpotable water, e.g., meeting drinking water standards. Other exemplaryapplications include sorbing heavy metals, such as mercury, from fluegases of coal- or oilfired power plants, mine drainage waters, orhydrocarbon streams such as petroleum streams. The sorbents of theinvention also remove H₂S and sulfide gases from effluent streams aswell as volatile organic compounds such as dioxins and furans.

The sorbent can be prepared by the sulfidation of red mud, whichcontains hydrated ferric oxides derived from the Bayer processing ofbauxitic ores. Sulfidation can be achieved by reacting the red mud withone or more sulfidizing compounds such as H₂S, Na₂S, K₂S, (NH₄)₂S, andCaS_(x). Unlike red mud, which is very hydrophilic, the sulfidized redmud is lyophobic and more readily dewatered. As a result, sulfidized redmud exhibits significantly faster filtration and settling rates thanthose exhibited by red mud.

The relative amount of the sulfidizing compound preferably is selectedso that the sulfur content of the reaction product is from about 0.2 toabout 10% above the residual sulfur content of the red mud. The weightratio of sulfidizing compound to red mud will vary on the type ofsulfidizing compound used and the desired level of sulfidation for aparticular end use. Most often, the sulfidizing compound and red mud arecombined at a weight ratio of from about 1:40 to about 1:4, more usuallyfrom about 1:25 to about 1:6, and even more usually from about 1:20 toabout 1:8.

The conditions under which the red mud can be sulfidized depend on suchfactors as the identity of the sulfidizing compound(s) and the intendeduse of the resulting sorbent. In some cases, sulfidation can beaccomplished by mixing red mud and the sulfidizing compound at ambienttemperature and atmospheric pressure. In general, higher sulfur contentscan be obtained when the reaction is carried out at elevatedtemperatures and/or elevated pressures. Sulfur content in the reactionproduct also can be influenced by factors such as the sulfur content ofthe sulfidizing agent. For example, compounds with higher sulfurcontents, such as calcium polysulfide, typically yield products havinghigher sulfur contents.

When using gaseous sulfidizing compounds, such as hydrogen sulfide(H₂S), it is often preferable to conduct the reaction at elevatedtemperature and/or elevated pressure to increase the rate of reactionand the sulfur content of the resulting sorbent. Suitable exemplaryreaction temperatures range from about 40 to about 200° C., often fromabout 80 to about 120° C. The reaction pressure typically ranges fromabout 1 to about 225 psi, often from about 30 to about 70 psi(absolute).

A particular use of the present technology resides in the treatment ofred mud, a by-product of the Bayer process in the production ofaluminum, the red mud being sulfidized according to the invention eitheras a stream of red mud exiting the bauxite treatment step or after aninitial storing of a red mud/caustic slurry. Such treatment permits morefacile recycling of at least portions of caustic liquor occurring as aportion of the red mud by-product due to the resulting sulfidized redmud having a less hydrophilic nature than does red mud per se.Accordingly, sulfidized red mud can be removed from the caustic liquormore easily by static sedimentation in settling ponds or by acceleratedsedimentation such as by use of hydroclassifiers including centrifugalor cyclonic action than can red mud. Sulfidized red mud can also be moreeasily removed from the caustic liquor by filtration than can red mud.

Treatment of waste water to reduce or remove phosphates, TDS (TotalDissolved Solids) including organic material and bacteria can also beeffected by the use of sulfidized red mud. In such treatment, it ispreferred to admix a slurry of sulfidized red mud with the waste waterfollowed by separation of the sulfidized red mud by separation processesincluding filtration, centrifugation, or sedimentation including staticsedimentation such as settling or accelerated sedimentation such as byhydroclassification. Use of sulfidized red mud in slurry form directlyafter sulfidization without filtering and drying is preferred for mostuse applications.

Drying of sulfidized red mud prior to use for waste water treatmentinter alia causes the sulfidized red mud to be less hydrophilic so thatsettling of the sulfidized red mud occurs more rapidly via staticsedimentation. Similarly, accelerated dewatering processes andfiltration processes also occur more rapidly when the sulfidized red mudis dried although sorbing activity is decreased. Concentration ofsulfidized red mud by sedimentation or filtration prior to drying can beefficacious and reduces the cost of drying.

Sulfidized red mud can also be spray-dried to particularly improvefiltration rates when such dried sulfidized red mud is used to form afiltration medium. In such applications, spray drying of sulfidized redmud improves filtration rate two or three-fold compared to spray dryingof red mud per se. Thermal exposure of the sulfidized red mud in a spraydrier at an outlet temperature of 100° C. for 15 to 30 seconds ispreferred. Spray-dried sulfidized red mud can advantageously be used tosorb contaminated water of toxic material including toxic metalsfollowed by separation of the sulfidized red mud from the resultingpurified water.

A slurry of sulfidized red mud such as can be produced by sulfidizationof red mud after discharge from a Bayer process exhibits enhancedutility relative to dried sulfidized red mud due to cost savingsoccurring through avoidance of filtration and drying stages, retentionof high alkalinity as can be lost in a filtration step, ease ofshipping, processing and mixing with a fluid which is to be treated withsulfidized red mud. In important uses of sulfidized red mud as asorbent, a slurry of sulfidized red mud can be used directly by bringingthe slurry into contact with a flue gas, acid mine waste streams orother fluid advantageously sorbed by sulfidized red mud. Further,shipping of a slurry of sulfidized red mud is comparable in cost toshipping dried sulfidized red mud.

Use of sulfidized red mud includes production of potable water throughtreating waste water; altering the hydrophilic nature of red mud toenhance dewatering of red mud; and, reduction of the size of red mudimpounds by enhanced removal of liquid from red mud once the red mud issulfidized.

In one embodiment of the present invention, the sorbent is slurriedtogether with the medium containing the contaminant(s) to be extracted.Suitable mixing equipment can be used to provide sufficient contactbetween the sorbent and the contaminant(s). The sorbent, which forms acomplex with the contaminant(s), can then be separated from the slurryusing one or more conventional techniques such as filtration,sedimentation, or centrifugation.

In an alternative embodiment of the present invention, the sulfidizedred mud sorbent is processed into pellets or the like using conventionalpelletizing or extrusion equipment. Preparing the sorbent in pellet formcan simplify its handling and/or use. The pellets may be incorporatedinto filters of conventional construction for use in a variety ofindustrial or consumer filtration applications, such as filters usablefor preparing potable water.

It has been found that the sulfidized red mud sorbent is effective forsorbing various contaminants, such as mercury, which are not effectivelysorbed by red mud. On the other hand, red mud is effective for sorbingother contaminants, such as arsenic, which are not effectively sorbed bysulfidized red mud. For the treatment of mediums having contaminants inboth of these categories, the use of red mud and sulfidized red mud intandem, either in the same sorbent composition or in sequentialtreatment stages (e.g., red mud followed by sulfidized red mud) can bemore effective than using either sorbent alone.

EXAMPLES Example 1

This example shows the preparation of red mud. A 1 kg sample of red mudreceived from Sherwin Alumina Company of Corpus Christi, Tex. wasslurried at 15% solids in demineralized water and filtered on a Buchnerfunnel. The resulting filter cake was re-slurried with demineralizedwater, re-filtered, and used as the starting material in Example 2. Thered mud thus prepared is used as detailed herein in remaining examples.

Example 2

This example illustrates the preparation of sulfidized red mud usinghydrogen sulfide (H₂S). Washed red mud (100 g) from Example 1 wasslurried in demineralized water at 15% solids and the stirred slurry wassaturated with hydrogen sulfide for 30 minutes at ambient temperature.The sample was dried overnight at 100° C. and the resulting cake waspulverized.

Example 3

This example shows the preparation of sulfidized red mud using H₂S underpressure in a Parr Bomb. The sulfidation procedure of Example 2 wasrepeated using a Laboratory Parr Bomb. After saturation of the slurrywith hydrogen sulfide gas, the bomb was sealed and heated four hours at100° C. while stirred. The bomb was then cooled, depressurized and thecontents filtered, dried, and pulverized.

Example 4

This example illustrates the preparation of sulfidized red mud usingammonium sulfide (NH₄)₂S. Red mud (200 g) was dispersed in 600 grams ofdeionized (DI) water in a Waring Blender for 5 minutes. Ammonium sulfide(10 g) was added and the slurry was heated with stirring on a hot platefor 1 hr. at 60° C. It was then filtered and dried at 90° C.

Example 5

This example shows the preparation of sulfidized red mud using sodiumsulfide (Na₂S). The procedure of Example 2 was repeated using sodiumsulfide instead of ammonium sulfide.

Example 6

This example illustrates the preparation of sulfidized red mud usingcalcium polysulfide (CaS_(x)). The procedure of Example 2 was repeatedusing 33.5 g of 30% solution of Cascade calcium polysulfide.

Example 7

The following table summaries the sulfur content of the red mud (RM) of

Code Description Example S (wt %) RM Red Mud 1 0.19 SRM-2 Sulfidized RedMud H₂S 2 0.48 SRM-3 Sulfidized Red Mud H₂S w/ Pressure 3 0.90 SRM-4Sulfidized Red Mud (NH₄)₂S 4 0.46 SRM-5 Sulfidized Red Mud Na₂S 5 0.62SRM-6 Sulfidized Red Mud CaS_(x) 6 1.19

A complete analysis of RM, SRM-3, SRM-4, SRM-5, SRM-6 is given in TableA below. The analysis reveals that filtration and washing duringpreparation of sulfidized red mud extracts sodium chloride (except forSRM-5) and reduces bound water in the red mud. It is notable that verysmall amounts of reacted sulfur have such a profound effect on thechemical and physical properties of red mud.

TABLE A Weight % Code Description Na₂O MgO Al₂O₃ SiO₂ P₂O₅ S Cl K₂O CoOTiO₂ MnO Fe₂O₃ BaO RM Control 4.73 0.12 17.1 8.23 1.14 0.19 0.20 0.066.79 6.12 0.73 39.9 0.02 SRM-3 H₂S (b) 3.94 0.14 14.6 9.14 1.38 0.900.11 0.05 6.36 6.79 0.90 46.2 0.02 SRM-4 (NH₄)₂S 4.39 0.13 17.9 9.241.26 0.46 0.15 0.04 8.82 6.95 0.85 42.3 0.02 SRM-5 Na₂S 5.20 0.11 17.28.56 1.15 0.62 0.15 0.03 7.53 6.22 0.75 41.5 0.02 SRM-6 CaS_(x) 4.440.09 16.2 8.41 1.29 1.19 0.14 0.04 9.32 6.60 0.81 41.2 0.02 PPM CodeDescription V Cr Co Ni W Cu Zn As Sn Pb Mo Sr U RM Control 1100 1258 99680 16 119 416 47 247 144 <10 424 65 SRM-3 H₂S (b) 1252 1506 121 860 23138 458 44 177 180 <10 498 57 SRM-4 (NH₄)₂S 1093 1379 120 762 30 146 64846 155 176 13 447 36 SRM-5 Na₂S 942 1272 103 695 24 130 504 31 181 15911 387 39 SRM-6 CaS_(x) 1054 1364 113 780 29 138 471 49 155 165 13 43150 PPM Code Description Th Nb Zr Rb Y RM Control 186 188 1757 24 673SRM-3 H₂S (b) 199 207 1503 21 831 SRM-4 (NH₄)₂S 159 153 1888 <10 748SRM-5 Na₂S 123 148 1659 <10 695 SRM-6 CaS_(x) 146 146 1767 <10 745

Example 8

This example illustrates leaching of red mud and sulfidized red mud. Inpart (a), a slurry of red mud (50 g) and demineralized water (450 ml)was prepared, mixed for 30 minutes, and filtered. The filtrate wasacidified with 2 ml concentrated nitric acid and analyzed by ICP usingEPA3050 and EPA6010 methods.

In part (b), the procedure of part (a) was repeated using sulfidized redmud from Example 2.

Results are given in Table I and show that leachate from sulfidized redmud (SRM) gave a lower content of heavy metals (low parts per billion)than leachate from the red mud (RM) in every case except Cd, where thedifference was insignificant.

TABLE I Metal Concentration in Leachate (ppm) Hg As Cd Cr Pb Se SRM0.0026 ND* 0.0013 0.0044 ND ND RM 0.0032 0.096 ND 0.0510 0.0064 0.017*ND—Not detectable, below limits

Example 9

This example shows mercuric ion (3.5 ppm) sorption by sulfidized redmud. Ten grams of sulfidized red mud from Example 3 was slurried 30minutes with 1 kg demineralized water containing 3.5 ppm mercury (5.66ppm mercuric nitrate). The slurry was filtered and analyzed for mercury(Hg⁺⁺) by ICP (Method EOA 245.1).

Example 10

This example illustrates mercuric ion (3.5 ppm) sorption by red mud.Example 9 was repeated using red mud.

Example 11

This example shows mercuric ion (22 ppm) sorption by sulfidized red mud.Example 9 was repeated using 22 ppm mercury (Hg⁺⁺).

Example 12

This example illustrates mercuric ion (22 ppm) sorption by red mud.Example 11 was repeated using red mud.

Example 13

This example shows mercuric ion (41 ppm) sorption by sulfidized red mud.Example 9 was repeated using 41 ppm mercury (Hg⁺⁺).

Example 14

This example illustrates mercuric ion (41 ppm) sorption by red mud.Example 13 was repeated using red mud.

Results of Examples 9-14 are summarized in Table II and demonstrate thesuperior performance of sulfidized red mud compared to red mud forsorption of mercuric ion from aqueous solutions.

TABLE II Mercuric Concentration Example In Filtrate Sorbent Control  3.5ppm none  9 0.56 ppm red mud 10  0.2 ppm sulfidized red mud Control 22.0ppm none 11  8.0 ppm red mud 12 0.22 ppm sulfidized red mud Control 41.0ppm none 13 23.4 ppm red mud 14 0.04 ppm sulfidized red mud

Example 15

This example shows mercury (metal) sorption from vapor phase bysulfidized red mud and by red mud (spray absorbed). In part (a), onegram of mercury metal was placed in a two necked round bottom (RB) flaskon a supported heating mantle. One neck of the flask was open and thesecond neck was connected with a Teflon® tube to an aperture in theinlet duct of a spray dryer. The mercury was heated to 300° C. while hotair was aspirated through the vessel. Mercury vapor was entrained in theair as it was drawn into the inlet air duct of the spray dryer heated to300° C. A slurry of 50 g SRM (Example 3) in 450 ml demineralized waterwas sprayed by a rotary atomizer operating at 30,000 rpm. The feed rateof SRM was regulated to produce an outlet temperature of 100° C. fromthe dryer.

In part (b), the procedure of part (a) was repeated using RM (Example 1)instead of SRM.

The mercury content of the spray dried SRM from part (a) and the RM frompart (b) are tabulated in Table III and demonstrate that the SRM had asignificantly improved sorption of mercury.

TABLE III Hg Concentration (ppm) 15(a) SRM-3 61.0 15(b) RM-1 8.1

SRM-3 absorbed 7.5 times as much mercury as RM-1 when spray dried at300° C. inlet and 100° C. outlet in the presence of an air streamcontacted by mercury heated to 250° C. Sulfidized red mud issignificantly superior to red mud as a sorbent for elemental mercurymetal vapor.

Example 16

This example shows mercury (metal) sorption from vapor phase bysulfidized red mud and by red mud (spray absorbed). Example 15 wasrepeated except that a slurry of 100 g SRM in 900 ml demineralized waterwas used. On completion of drying, a 50 g sample (a) was set aside foranalysis and 50 g was re-slurried in 450 ml demineralized water andre-dried (b). Samples 16a and 16b were analyzed for mercury.

This experiment was then repeated using 100 g RM to furnish samples 16cand 16d, which were analyzed. The results of parts (a)-(d) are shown inTable IV below.

TABLE IV Hg Concentration (ppm) 16(a) SRM-3 1st pass 95 16(b) SRM-3 2ndpass 340 16(c) RM-1 1st pass 43 16(d) RM-1 2nd pass 48

As evident from Table IV, SRM-3 was more than twice as efficient as RM-1on the first pass and about seven times as efficient as RM-1 on thesecond pass. The results show that the affinity of SRM-3 for mercuryimproves with increased exposure to mercury, indicating an inductioneffect.

Example 17

This example illustrates mercury (metal) sorption from vapor phase bysulfidized red mud (a) and red mud (b) using a column. In part (a), onegram of mercury was placed in a two necked RB flask supported on aheating mantle. One neck of the flask was open (vented) and the secondneck was connected to a vertical tube 20 cm long and 2.5 cm diameterhalf filled with spray dried sulfidized red mud. A slight vacuum wasapplied to the open end of the packed tube and regulated to fluidize thespray dried sulfidized red mud while the mercury in the flask was heatedto 300° C. The aspiration was continued for 20 minutes, the tube wasdisconnected from the RB flask and the sulfidized red mud contentsanalyzed for mercury by ICP.

In part (b), the procedure of part (a) was repeated using spray driedred mud, after which the red mud was also submitted for mercury analysisby ICP.

Results of the above experiment are tabulated in Table V and demonstrateincreased sorption of mercury vapor by sulfidized red mud (SRM-3)compared to red mud (RM-1).

TABLE V Hg Concentration (ppm) 17(a) SRM-3 72 17(b) RM-1 25

Example 18

This example shows sorption of mercury (metal) from naphtha bysulfidized red mud (a) and red mud (b). In part (a), a solution of 500ml naphtha containing 100 ppb of mercury was slurried with 10 grams ofspray dried sulfidized red mud (SRM) for 30 minutes. The resultingslurry was filtered, and the SRM filter cake was dried for 1 hour atroom temperature and analyzed for mercury by ICP.

In part (b), the procedure of part (a) was repeated using red mud (RM).

Results of parts (a) and (b) are shown in Table VI and reveal theincreased capture of mercury from naphtha by sulfidized red mud (SRM-3).

TABLE VI Mercury (ppb) 18(a) SRM-3 filtrate 46 18(b) RM-1 filtrate 21

Example 19

This example shows sorption of chromium (III) by sulfidized red mud(SRM) and red mud (RM). In part (a), ten grams of SRM was slurried 30minutes with 1 kg demineralized water containing 2.240 ppm chromium III.The slurry was filtered and the filtrate analyzed for chromium by EPA200.9 method.

In part (b), the procedure of part (a) was repeated using 2.240 ppmchromium III and red mud (RM). The results are shown in Table VII below.

TABLE VII Chromium III (ppm) Control 2.240 19(a) SRM-3 filtrate 0.00519(b) RM-1 filtrate 0.018

Results shown in Table VII demonstrate improved sorption of Chromium IIIby SRM-3 compared to RM-1.

Example 20

This example illustrates sorption of cobalt (II) by sulfidized red mud(SRM) and by red mud (RM). The procedures of Examples 19(a) and (b) wererepeated using 2.75 ppm of cobalt II. The results are shown in TableVIII below.

TABLE VIII Cobalt II (ppm) Control 2.75 20(a) SRM-3 filtrate 0.013 20(b)RM-1 filtrate 0.046

Results in Table VIII show that SRM-3 has greater affinity for cobalt IIthan RM1, with the filtrate from SRM-3 containing less than ⅓ of cobaltII than that contained in the filtrate from RM-1.

Example 21

This example shows sorption of nickel (II) by sulfidized Red Mud (SRM)and by red mud (RM). The procedures of Examples 15(a) and (b) wererepeated using 1.13 ppm nickel (II). The results are shown in Table IXbelow.

TABLE IX Nickel II (ppm) Control 1.13 21(a) SRM-3 filtrate 0.056 21(b)RM-1 filtrate 0.009

The results show nickel removal by SRM-3 was less efficient than byRM-1.

Example 22

This example illustrates sorption of copper (II) by sulfidized red mud(SRM-3) and by red mud (RM-1). The procedures of Examples 19(a) and (b)were repeated using 1.550 ppm, 6.250 ppm, and 30.500 ppm copper (II).The results are shown in Table X below.

TABLE X Copper II (ppm) Control A 1.550 22(a) SRM-3 filtrate <0.00422(b) RM-1 filtrate 0.028 Control B 6.250 22(c) SRM-3 filtrate 0.03822(d) RM-1 filtrate 0.054 Control C 30.500 22(e) SRM-3 filtrate 0.04022(f) RM-1 filtrate 0.073

The results show a clear advantage of SRM-3 over RM-1 for copper removalover a 15-fold range of copper concentrations.

Example 23

This example shows sorption of zinc (II) by sulfidized red mud (SRM) andby red mud (RM). The procedures for Examples 15(a) and (b) were repeatedusing 1.850 ppm zinc (II) and 2.380 ppm zinc (II). The results are shownin Table XI below.

TABLE XI Zinc II (ppm) Control A 1.850 23(a) SRM-3 filtrate 0.009 23(b)RM-1 filtrate 0.035 Control B 2.380 23(c) SRM-3 filtrate 0.022 23(d)RM-1 filtrate 0.103

The results show SRM-3 is superior to RM-1 for zinc removal and yieldsfiltrates with about one-fourth the concentration of zinc.

Example 24

This example illustrates sorption of silver (I) by sulfidized red mud(SRM). The procedure of Example 15(a) was repeated using 3.15 ppm silver(I). The results are shown in Table XII below.

TABLE XII Silver I (ppm) Control 3.15 24(a) SRM-3 filtrate N.D.

The results demonstrate that SRM-3 is an excellent sorbent for silverion.

Example 25

This example shows sorption of gold I by sulfidized red mud (SRM). Theprocedure of Example 19(a) was repeated using 0.703 ppm gold III. Theresults are shown in Table XIII below.

TABLE XIII Gold III (ppm) Control 0.703 25(a) SRM-3 filtrate 0.227

The results demonstrate that SRM-3 is a good sorbent for gold (III) inthat 68% is sorbed.

Example 26

This example illustrates sorption of cadmium II by sulfidized red mud(SRM) and by red mud (RM). The procedures of Examples 19(a) and (b) wererepeated using 1.850 ppm cadmium. The results are shown in Table XIVbelow.

TABLE XIV Cadmium II (ppm) Control 1.850 26(a) SRM-3 filtrate 0.00926(b) RM-1 filtrate 0.035

The results show that SRM-3 is significantly more efficient in removingcadmium II from water than is RM-1.

Example 27

This example shows sorption of lead ion ⁺2 by sulfidized red mud (SRM)and by red mud (RM). The procedures of Examples 19(a) and (b) wererepeated using 2 ppm lead ion (⁺2). The results are shown in Table XVbelow.

TABLE XV Lead II (ppm) Control 2.0 27(a) SRM-3 filtrate 0.007 27(b) RM-1filtrate 0.058

The results show that SRM-3 reduced lead content to about one-eighth ofthe content achieved by RM-1. The lead content of the SRM filtrate (7ppb) met drinking water standards (currently 15 ppb).

Example 28

This example shows sorption of selenium by sulfidized red mud (SRM) andred mud (RM). The procedures of Examples 19(a) and (b) were repeatedusing 2.5 ppm selenium. The results are shown in Table XVI below.

TABLE XVI Selenium (ppm) Control 2.5 28(a) SRM-3 filtrate 0.24 28(b)RM-1 filtrate 2.10

The results show that SRM-3 reduced Se by about 90% while RM-1 onlyreduced Se by about 16%.

Example 29

This example illustrates sorption of uranium by sulfidized red mud(SRM-3) and red mud (RM-1). The procedures of Examples 19(a) and (b)were repeated using a Uranium Atomic Absorption Standard Solutioncontaining 1000 micrograms of U (as uranyl nitrate—UO₂(NO₃)₂) and madeup in varying concentrations (1.13, 10.1, and 38.0 ppm), and thentreated with sulfidized red mud (SRM-3) and red mud (RM-1). In addition,a third test was performed on each uranium solution using a mixture of 5g sulfidized red mud (SRM-3) and 5 g red mud (RM-1). The results areshown in Table XVII below.

TABLE XVII Uranium (ppm) Control A 1.13 29(a) SRM-3 filtrate 0.040 29(b)RM-1 filtrate 0.074 29(c) RM-1/SRM-3 0.031 Control B 10.1 29(d) SRM-3filtrate 0.494 29(e) RM-1 filtrate 2.450 29(f) SRM-3/RM-1 filtrate 1.610Control C 38.0 29(g) SRM-3 filtrate 3.950 29(h) RM-1 filtrate 6.90029(i) SRM-3/RM-1 filtrate 4.660

The data in Table XVII (29(f)-(i)) confirm that sulfidized red mud issignificantly more efficient for extraction of uranium than is red mud.Moreover, combinations of sulfidized red mud and red mud (1:1) are moreeffective than red mud alone. The combination of SRM and RM allows thecomplimentary extraction of elements while eliminating the leaching ofother elements from RM.

Table XVIII below summarize the results of Examples 19-27. The lastcolumn indicates the amount (in wt %) of the target material that wasremoved by SRM.

TABLE XVIII % Control Removed Example Element (ppm) RM (ppm) SRM (ppm)by SRM 19 Chromium 2.240 0.018 0.005 99.997 III 20 Copper II 1.550 0.028<0.004 99.997 Copper II 6.250 0.054 0.038 99.993 Copper II 30.500 0.0730.040 99.999 21 Zinc II 1.850 0.035 0.009 99.995 Zinc II 2.380 0.1030.022 99.990 22 Silver I 3.15  ND* ND 99.999 23 Gold I 0.703 ND 0.22767.7 24 Cadmium II 1.850 0.035 0.009 99.995 25 Lead II 2.0 0.058 0.00799.996 28 Selenium 2.5 2.1 0.24 99.904 29 Uranium II 1.13 0.074 0.0499.964 Uranium II 10.1 2.45 0.494 99.951 Uranium II 38.0 6.90 3.9599.896 *ND = not detectable

Example 30

This example compares SRM and RM for sorption of As, Co, Mn, and Sr. Theprocedure of Example 9 was repeated using solutions of arsenic (III),arsenic (V), cobalt II, manganese (II), and strontium (I), with resultssummarized in Table XIX.

TABLE XIX Control RM-1 % SRM-3 % Element (ppm) ppm Removed Ppm RemovedArsenic III 0.60 0.11 81.7 0.36 60.0 Arsenic V 1.60 0.21 87.8 1.15 72.0Cobalt II 2.75 0.013 99.5 0.046 98.3 Manganese II 1.63 0.135 91.7 0.54866.4 2.10 0.72 65.7 0.792 37.7 Strontium II 1.90 0.10 94.7 1.10 42.1 9.00.08 99.1 4.60 48.9 27.0 0.19 99.3 11.0 59.2

These experiments reveal that the efficiency of red Mud (RM-1) issignificantly better than SRM-3 in the case of As (III), As (V), Mn(II), and Sr (II). However, the use of red mud as a sorbent is limitedby the leaching of undesirable elements which can and have causedserious problems. Use of sulfidized red mud in combination with red mudallows utilization of the latter because sulfidized red mud sorbsundesirable leaching of extraneous metals from red mud itself.

Example 31

This example shows sorption of Hg (II) by various sulfidized red muds,as summarized in Table XX below.

TABLE XX Concentration of Hg (II) in Leachate (ppm) Concentration of Hg(II) in SRM-4 SRM-5 SRM-6 SRM-3 Original 5% % 5% % 5% % H₂S % solution(ppm) (NH₄)₂S Removed Na₂S Removed CaS_(x) Removed pressure Removed 4.50.001 100 0.449 90.0 0.005 99.9 0.004 99.9 19.6 0.0229 99.9 15.4 21.43.16 83.8 0.02 99.9

Each of SRM-3, -4, and -6 gave excellent sorption results from solutionsof Hg (II) at two concentration (4.5 ppm and 19.6 ppm). It issignificant that SRM-4 reduced Hg to 1 ppb, thus meeting currentdrinking water standards (2 ppb maximum). SRM-5 made form red mud bytreatment with Na2S was much less efficient. Ammonium sulfide treatment(SRM-4) was the most effective sorbent despite the fact it had thelowest S content as shown by the analysis in Example 7.

Example 32

This example illustrates treating mercury metal with red mud andsulfidized red mud (wet). In part (a), a mixture of 10 g mercury metal,50 g red mud, and 100 g demineralized water was rapidly mixed in aWaring Blender for 10 minutes. The aqueous slurry of red mud wasseparated from mercury in a separatory funnel. The slurry was filtered,dried at 80° C. for 4 hours, then ground in a coffee grinder for 3minutes, and submitted for mercury analysis.

In part (b), the procedure of part (a) was repeated using SRM-2. In part(c), the procedure of part (a) was repeated using SRM-410, which wasprepared by reaction of red mud and 10% ammonium sulfide. Results forparts (a)-(c) are shown in Table XXI below.

TABLE XXI Example Reagent % Hg sorbed 32(a) RM-1/Hg 1.27 32(b) SRM-2/Hg0.55 32(c) SRM-410/Hg 1.65

The results show that sulfidized red mud SRM-410 of Example 32(c) wasabout 30% more effective than red mud (RM-1) in sorbing mercury.

Example 33

This example illustrates treating mercury metal with red mud andsulfidized red mud (dry). In part (a), a mixture of 10 g mercury metaland 50 g red mud was rapidly mixed in a Waring Blender for 10 minutes.Demineralized water (100 g) was added to the mixture and mixing in theblender resumed for 5 minutes. The aqueous slurry of red mud wasseparated from mercury in a separatory funnel. The slurry was filtered,dried at 80° C. for 4 hours, then ground in a coffee grinder for 3minutes, and submitted for mercury analysis.

In part (b), the procedure of part (a) was repeated using SRM-2. In part(c), the procedure of part (a) was repeated using SRM-410, which wasprepared as described in Example 32 above. The results are provided inTable XXII below.

TABLE XXII Example Reagent % Hg sorbed 33(a) RM-1/Hg 1.84 33(b) SRM-2/Hg6.34 33(c) SRM-410/Hg 5.58

The results show that sulfidized red mud SRM-2 and SRM-410 sorbed overthree times as much mercury than did red mud (RM-1). The sorptionprocedure in Example 33, which used direct contact of the sulfidized redmud and mercury (without water present initially), was much moreeffective than the procedure in Example 32, which initially added waterto the mercury and sulfidized red mud.

Example 34

This example shows sorption of thorium (IV), as Th(NO₃)₄·H₂O, by RM-1and SRM-3. In part (a), 10 g of sulfidized red mud (SRM-4) was slurriedfor 30 minutes with 1 kg demineralized water containing 1 ppm thorium.The slurry was filtered and analyzed for thorium.

In part (b), the procedure of part (a) was repeated using 5 ppm thorium.In part (c), the procedure of part (a) was repeated using 10 ppmthorium. In part (d), the procedure of part (a) was repeated using 20ppm thorium. The procedures of parts (a)-(d) were then repeated usingred mud. The results are summarized in Table XXIII below.

TABLE XXIII Th (ppm) in Leachate Example Control SRM-4 RM-1 34(a) 0.956ND* 0.051 34(b) 4.930 ND 0.260 34(c) 10.500 ND 0.564 34(d) 19.400 ND0.921 *ND = not detectable

The results show that sulfidized red mud SRM-4 was very effective(essentially quantitative) for thorium sorption.

Example 35

This example compares sedimentation rates of SRM-3 and RM-1. In thecourse of tests on metal sorption from aqueous solutions by sulfidizedred mud and red mud, it was found that in all cases, sulfidized red mudexhibited significantly faster filtration rates than red mud. Red mud isvery hydrophilic but conversion of red mud to sulfidized red mudtransforms it to a lyophobic particle which is more readily dewatered.The unexpected improvement of dewatering behavior is shown in thefollowing experiment:

A dispersion of 50 grams of RM-1 in 500 ml demineralized water wasprepared by rapid mixing in a Waring Blender for 10 minutes. Theexperiment was repeated using 50 grams of SRM-3 in 500 ml demineralizedwater.

Both freshly prepared slurries were allowed to settle undisturbed atambient temperature (25° C.) for a period of 72 hours. After 72 hours,the RM-1 dispersions had settled to give a clear supernatant layer ofonly 1 cm. The remaining slurry consisted of dispersed RM-1 with novisible sediment.

During the 72 hour period, the SRM-3 slurry completely settled tofurnish a sedimentary layer about 1 cm deep and a clear supernatantlayer 11.5 cm above the sediment.

These results clearly show the total alteration of surface chemistry andimproved dewatering characteristics of red mud by relatively smalldegrees of sulfidation.

Example 36

Five kilograms of sulfidized red mud from Example 4 was mixed with threekilograms of water containing 50 grams of sodium silicate in a rotatingspherical pelletizer (candy pan) for 30 minutes and then screened toreject and recycle plus 6 mm and minus 3 mm particles. The resultingpellets were dried for four hours at 110° C. The pellets were packed ina filter bed 60 cm deep and used to filter dilute solutions of heavymetals.

Example 37

A sample of red mud as prepared according to Example 1 is taken toconstitute Sample A, a control untreated red mud that had not beensulfidized. Sample B was prepared by sulfidizing red mud (A) at 121° C.and at a pressure of 30 psi in a Parr Bomb using H₂S as the sulfidizingagent as in Example 3. Table XXIV illustrates the results of analysis byThe Mineral Lab, Inc. using X-Ray Diffraction.

TABLE XXIV Approx. Wt % Mineral B (Sulfidized Name Chemical Formula A(Red Mud) Red Mud) Hematite Fe₂O₃ 37 22 Goethite FeO(OH) 10 10 GibbsiteAl(OH)₃ <10 15 Boehmite AlOOH — — Calcite CaCO₃ <10 <10 Anatase TiO₂ <3— Perovskite CaTiO₃ — <10 Ilmenorutile (Ti,Nb,Ta,Fe)O₂ —  <5?Pseudorutile Fe₂Ti₃O₉ —  <5? Rutile TiO₂ — — Quartz SiO₂ — — —CaTi₃Al₈O₁₉ — — — Na₈Al₆Si₆O₂₄SO₄•3H₂O 17 <10 Amorphous — <20 <25Unidentified — <5  <5

The results of the analysis shows that each of the Samples A and Bcontained amorphous material. Pyrrhotite was not detected in Sample B, amaterial that is the reaction product of the sulfidization of red mud astaught herein.

Example 38

The procedure detailed in Example 1 was repeated with substitution ofred mud received from Noranda Aluminum Company of Gramercy, La. for thered mud received from Sherwin Alumina Company. The Noranda red mud wasanalyzed for moisture content and found to be 53.8% solids. Two slurriesof the Noranda red mud having 25% solids with volumes of six (6) literswere made up, the weight of each slurry being approximately 7.54kilograms. The slurries were respectively referred to as Sample A andSample B. Sample A was mixed at high speed for four hours using alaboratory stirrer. The pH of Sample A was measured to be 10.34. SampleB was treated with 500 grams of 20% ammonium sulfide solution and theadmixture was heated to 60° C. for one hour and allowed to cool to roomtemperature. The resulting slurry containing sulfidized red mudexhibited a pH of 9.48, this sulfidized slurry being referred to assulfidized Sample B. A portion of Sample A and a portion of sulfidizedSample B were each vacuum filtered, the filtrates reslurried to 25%solids and spray dried. Particle size analysis of the resulting spraydried materials indicated no significant difference in particle sizes inthe two resulting slurries.

Example 39

In preparation for testing of Sample A and Sulfidized Sample B forExample 38, 10 ml of 0.14N mercury (II) nitrate solution was added to 5liters of distilled water. One liter of the resulting solution wasreserved as a control designated hereinafter as 062711-A.

Example 40

Sample 062711-B was prepared to contain 40 grams of 25% solidssulfidized red mud slurry taken from Sulfidized Sample B from Example38. Sample 062711-B, unfiltered and undried, was diluted to one liter ofliquid using water.

Example 41

Sample 062711-C was prepared to contain 10 grams of filtered andspraydried material derived from Sulfidized Sample B from Example 38 in oneliter of water.

Example 42

Sample 062711-D was prepared to contain 40 grams of 25% solids takenfrom Sample A from Example 38, the slurry of Sample A not having beenfiltered or dried, in one liter of distilled water.

Example 43

Each of the Samples prepared in Examples 39 through 42 were mixed in aWaring Blender for 5 minutes, filtered using Whatman 54 paper, andfiltered once more using a Millipore filter equipped with a membranewith 2 cc of 70% nitric acid being added to each sample as a stabilizerprior to shipment for resting at Altamaha Laboratories.

Table XXV provides mercury sorption test results:

TABLE XXV Sample Mercury ppm Control 062711-A 37.00 10 ml of 0.14NMercury (II) Nitrate solution added to 10 kilograms of distilled water062711-B 0.000919 Sulfidized Red Mud Slurry: Not Filtered or Dried 40grams of 25% solids sulfidized red mud slurry diluted to one liter ofslurry 062711-C 0.0874 Sulfidized Red Mud Slurry: Filtered and Dried 10grams of filtered and spray dried sulfidized red mud diluted to oneliter of slurry 062711-D 2.27 Red Mud Slurry: Not Filtered or Dried 40grams of 25% solids red mud slurry diluted to one liter of slurry

Conclusions evident from Table XXV are that sulfidized red mud that isnot filtered and dried, Sample 062711-B, was approximately ten timesmore efficient in sorbing mercury than the same slurry that waspreviously filtered and dried, Sample 062711-C. Both samples 062711-Band 062711-C were significantly more efficient in sorbing mercurycompared to unsulfidized red mud, Sample 062711-D.

Two slurries of ten grams each respectively of spray dried red mud andspray dried sulfidized red mud in one liter of distilled water wereprepared using a Waring blender for five minutes. Each slurry was pouredseparately into a Buchner funnel equipped with a Whatman 54 paper andvacuum was applied. Filtration of the liquid from the slurry of red mudrequired 17.5 minutes while filtration of the liquid from the sulfidizedred mud slurry required 5.0 minutes.

Red mud has previously been suggested as a component of a sorbing agentfor wastewater treatment. Lopez et al in Wat. Res. Vol. 32, No. 4, pp.1314-1322, 1998 combined red mud with CaSO₄ to form aggregates stable inaqueous media, these aggregates being used to sorb impurities fromwastewater streams. However, Lopez et al did not address the problem ofheavy metal shedding from such aggregates or from red mud itself whenused as a sorbent particularly in aqueous systems.

Use of sulfidized red mud for treatment of waste effluent streams andparticularly waste waters including sewage at various stages oftreatment improves over the use of red mud whether or not aggregatedwith other substances by the fact that sulfidized red mud does notrelease heavy metals into the effluent streams. As noted herein, the useof sulfidized red mud in effluent treatment including wastewatertreatment such as sewage treatment exhibits a number of othersignificant advantages and improvements over prior sorbing processes andagents.

Sulfidized red mud as disclosed herein is particularly useful in thetreatment of sanitary waste water in the removal or reduction of TDS(Total Dissolved Solids) and phosphorus. Such treatment of sanitarywaste water from typical oxidation ponds results in reduction of TDS andP, results consistent with the sorptive properties of sulfidized red mudfor various contaminants in water. As with uses previously described andas described herein, a red mud slurry can be directly sulfidized andused as produced without filtration or drying.

Example 44

A control sample and a test sample of sanitary waste water taken fromOxidation Pond 1 at New Hope Plantation Mobile Home Park, Brunswick,Ga., were tested. The control sample was not treated and thus is labeled“Untreated” in Table XXVI. The untreated control sample was tested forTDS, P and Fecal Coliform bacteria. The test sample was shaken with 10%by weight of sulfidized red mud containing 25% solids, 5% (NH₄)₂S basedon red mud for ten minutes. The results were obtained with a singletreatment.

TABLE XXVI Treated with Detection Units Untreated Sulfidized Red MudLimit TDS mg/liter 89 71 5.0 P mg/liter 1.17 0.359 0.1 Fecal mpn/100 ml≧1600 ≧1600 2.0 Coliform

As taught in U.S. application Ser. No. 12/796,066, filed Jun. 8, 2010,by the same inventor and incorporated in its entirety hereinto byreference, high quality water suitable for distribution and consumptionby humans and animals as well as for use in industrial processes isproduced by the removal of discolored organic compounds through use ofsulfidized red mud as an effective sorbent. Discolored organic compoundsare contaminants of aqueous streams such as discharges from foodprocessing, mining waste inter alia as well as transportation, sewageand storm runoff. Environmental regulations have been enacted to assureaesthetic appearance of public waterways by setting color standards forindustrial discharges such as from paper mills and the like. Removal orreduction of concentrations of discolored organic compounds isaccomplished according to present teachings in a manner similar to thatdisclosed herein for treatment of waste waters for removal of a varietyof contaminants present in water.

Compounds considered to be undesirable discolored organic compoundsinclude but are not limited to humic acids, fulvic acids, tannins andorganic compounds formed by degradation of plant residues as well asorganic compounds formed during industrial processes such as pulping andpaper manufacture. These compounds and materials are very hydrophilicand not easily separated from water. Other natural and industrialcontaminants found in surface and subsurface water include phthalates,bisphenol compounds, hormones, insecticides, herbicides andpharmaceutical and illicit drug residues. Removal of such compounds byreadily operable and low cost processing is possible through treatmentof aqueous solutions containing such compounds and materials asdescribed herein.

Treatment of a medium containing discolored organic compounds as well asother contaminants is effected by contacting the medium with a sorbentcomprising sulfidized red mud and separating the sorbent from themedium. The sorbent, containing adsorbed contaminants, can be separatedfrom the medium using techniques including sedimentation, filtration andcentrifugation. A sorbent containing or comprising sulfidized red mudcan be slurried with the medium containing contaminants. The sorbent canalternatively be provided in the form of pellets or the like throughwhich the medium is passed. Amounts of sulfidized red mud used inprocessing can vary over a wide range depending on factors such as theidentity and relative amounts of the contaminant or contaminants presentin the medium. Relatively small quantities of discolored organiccompounds, for example, can be effectively sorbed with relatively smallquantities of sulfidized red mud. By way of example, the amount ofsulfidized red mud may range from about 0.005 to be 0.5 grams permilliliter of medium and often ranges from about 0.01 to about 0.1 gramper milliliter.

The extent to which a contaminant or contaminants may be removed from amedium will vary depending on such factors as whether the process isintended to produce potable water. The extent of removal may bequantified using any known technique. In the case of removal ofdiscolored organic compounds, colorimetric scales are typically used,such as color value (CV) and/or absorbance. The extent of removal ofcontaminants may be increased, for example, by implementing multiplepasses or stages as needed to achieve desired optical properties and/orpurity.

Example 45

This example illustrates clarification of Okefenokee Swamp water withsulfidized red mud. 500 ml of Okefenokee Swamp water (Sample I) wasadjusted to pH 7 with dilute NaOH and mixed with 10 grams of sulfidizedred mud (SRM) made with 10% ammonium sulfide in a Waring blender at highspeed for 5 minutes. The mixture was transferred to a beaker and allowedto stir an additional hour using a magnetic stirrer. The suspension wasfiltered and the color value of the filtrate was determined with aLaMotte TC-3000e colorimeter. Another 10 grams of sulfidized red mud(SRM) was then added and the procedure was repeated a second time(2^(nd) Pass). The filtrate was again evaluated for color. Results aregiven in Table XXVII and showed that the treated sample was nearlycolorless.

TABLE XXVII Absorbance Testing of Okefenokee “Black” Water (Sample I)Sample Designation Color Value (CV) (375 mm) Control (untreated) 3471^(st) Pass SRM 38.9 2^(nd) Pass SRM 18.8

Another sample of Okefenokee “Black” Water (Sample II) was treated withsulfidized red mud according to the above procedure. The absorbance wasreduced 90% to nearly colorless, as shown in Table XXVIII.

TABLE XXVIII Absorbance Testing of Okefenokee “Black” Water (Sample II)Sample Designation Absorbance* Control (untreated) 0.063 Sample II0.0063 *Fisher Genesys5 Spectrophotometer 500 mm

While particular embodiments of the present invention have beendescribed and illustrated, it should be understood that the invention isnot limited thereto since modifications may be made by persons skilledin the art. The present application contemplates any and allmodifications that fall within the spirit and scope of the underlyinginvention disclosed and claimed herein.

1. A process of dewatering red mud, comprising reacting the red mud tobe dewatered with a sulfidizing compound at a reaction temperature of upto about 200° C. and a reaction pressure from atmospheric pressure up toabout 30 psi to form a dispersion of sulfidized red mud in water, wherethe step of reacting comprises combining the sulfidizing compound withthe red mud at a weight ratio of from about 1:40 to about 1:4, andallowing the dispersion to settle for a sufficient time to form asedimentary layer and a supernatant layer.
 2. The process of claim 1 andfurther comprising separating the sedimentary layer comprised ofsulfidized red mud from the supernatant layer.
 3. The process of claim 2wherein the sedimentary layer is separated from the supernatant layerusing at least one of filtration and centrifugation.
 4. The process ofclaim 1 wherein the dispersion is allowed to settle under the influenceof gravity.
 5. The process of claim 1 wherein the sulfidized red mud isdevoid of pyrrhotites.
 6. The process of claim 1 wherein the sulfidizedred mud is formed in a system absent added hydrogen molecules.
 7. Theprocess of claim 1 wherein the sulfidized red mud contains from about0.2 to about 10 weight percent sulfur above residual sulfur initiallypresent in the red mud prior to reaction with the sulfidizing compound.8. The process of claim 1 wherein the sulfidizing compound is selectedfrom the group consisting of H₂S, Na₂S, K₂S, (NH₄)₂S, CaS_(x) andcombinations thereof.
 9. The process of claim 1 wherein the sulfidizedred mud is formed at a reaction temperature from ambient temperature upto about 60° C.
 10. The process of claim 1 wherein the sulfidized redmud is formed at ambient temperature.
 11. A method for processing aslurry of red mud and water, comprising reacting the red mud with asulfidizing compound at a reaction temperature of up to 200° C. and areaction pressure from atmospheric pressure up to about 30 psi to form asulfidized red mud, where the step of reacting comprises combining thesulfidizing compound with the red mud at a weight ratio of from about1:40 to about 1:4, filtering the sulfidized red mud to form a filtercake, and drying the filter cake at a temperature of at least 100° C.for at least 30 minutes.
 12. The method of claim 11 wherein the filtercake is dried for at least 120 minutes.
 13. The method of claim 11wherein the sulfidized red mud is devoid of pyrrhotites.
 14. The methodof claim 11 wherein the sulfidized red mud is formed in a system absentadded hydrogen molecules.
 15. The method of claim 11 wherein thesulfidized red mud contains from about 0.2 to about 10 weight percentsulfur above residual sulfur initially present in the red mud prior toreaction with the sulfidizing compound.
 16. The method of claim 11wherein the sulfidizing compound is selected from the group consistingof H₂S, Na₂S, K₂S, (NH₄)₂S, CaS_(x) and combinations thereof.
 17. Amethod for processing a slurry of red mud and water, comprising reactingthe red mud with a sulfidizing compound at a reaction temperature of upto 200° C. and a reaction pressure from atmospheric pressure up to about30 psi to form a sulfidized red mud, where the step of reactingcomprises combining the sulfidizing compound with the red mud at aweight ratio of from about 1:40 to about 1:4, centrifuging the slurry toform a layer of sulfidized red mud and a supernatant layer, removing thesupernatant layer from the layer of sulfidized red mud, and drying thelayer of sulfidized red mud at a temperature at least 100° C. for atleast 30 minutes.
 18. The method of claim 17 wherein the layer ofsulfidized red mud is dried for up to 120 minutes.
 19. The method ofclaim 17 wherein the sulfidizing compound is selected from the groupconsisting of H₂S, Na₂S, K₂S, (NH₄)₂S, CaS_(x) and combinations thereof.20. The method of claim 17 wherein the sulfidized red mud contains fromabout 0.2 to about 10 weight percent sulfur above residual sulfurinitially present in the red mud prior to reaction with the sulfidizingcompound.
 21. In a process wherein bauxite ores are treated in theproduction of alumina with a red mud slurried in a highly caustic liquorbeing produced as a by-product, the improvement comprising the steps of:sulfidizing the red mud slurried with the caustic liquor to form aslurry of sulfidized red mud and caustic liquor, the red mud beingsulfidized by reacting the red mud with a sulfidizing compound at areaction temperature of up to about 200° C. and a reaction pressure fromatmospheric up to about 30 psi; where the step of reacting comprisescombining the sulfidizing compound with the red mud at a weight ratio offrom about 1:40 to about 1:4; and, separating the sulfidized red mudfrom at least portions of the caustic liquor.
 22. In the process ofclaim 21 wherein the improvement further comprises the steps ofrecycling the at least portions of the caustic liquor to treatment ofthe bauxite ores.
 23. In the process of claim 21 wherein the separatingstep comprises static sedimentation.
 24. In the process of claim 21wherein the separating step comprises accelerated sedimentation bycentrifugal or cyclonic hydroclassification.
 25. In the process of claim21 wherein the improvement further comprises placing the sulfidized redmud and at least portions of the caustic liquor in a settling pond.